This invention relates to telecommunication networks, in particular to allocation of resources in a stratified reference model.
A stratified reference model is a generalization of the OSI reference model that enables a description of complicated network-on-network structures. Each network level is referred to as a stratum. A stratum is a logical model of a physical transmission network. A stratum describes nodes and routes between the nodes. The physical transmission network modelled by a stratum comprises nodes and links. Links are grouped into trunks which extend between the nodes. The various stratum networks are defined by configuration data. The different strata together make up a stratified transport network. Each stratum is associated with a respective bearer service. By bearer service is meant a service providing transport of data. Different strata have different bearer services.
In order to avoid misconceptions the following definitions are used: A connection is used to transfer information between two end points. A connection is created in various ways. For example a connection is created by cross connection, by manual switching or by switching. Cross connected connections are created in for example cross connecting devices, manually switched connections are created for example in connector matrixes by soldering and switched connections are created on demand, for example by dialling a directory number on a telephone.
A channel is a means for unidirectional transmission. A channel is used to carry information from one point to another. To transmit information from A to B one channel is required, said one channel having a direction from A to B. To transmit information from B to A another channel is required, said another channel having the opposite direction of said one channel.
Two oppositely directed channels extending between the same pair of points are in the following referred to as a channel pair. Several channel pairs together make up a link. A link is a physical system (that transports information). Accordingly, a link carries channel pairs. The maximum number of channel pairs a link can carry depends on the bearer service and on the properties of the physical system.
A route is a logical conception. A route comprises a number of channel pairs and is used to interconnect two nodes. In theory there is no maximum number of channel pairs a route can comprise. The conception of route is used to define the way a connection follows between nodes of a stratum. This is referred to as routing and is conventional.
At each end of a link there is an exchange terminal ET. An ET operates to "insert" or multiplex together a number of channel pairs on one and the same link and to "extract" or demultiplex channel pairs from said same link.
The above definitions are explained in connection with FIG. 1 and FIG. 2. In FIG. 1 there is one route R1 extending between two nodes N1 and N2. As an example route R1 carries 96 channels so distributed that there are 48 channels in each one of two opposite directions, i.e. route R1 carries 48 channel pairs. FIG. 1 is a logical description of the physical transmission system shown in FIG. 2. In FIG. 2 there are two links L1 and L2 extending between nodes N1 and N2. At each end of links L1 and L2 there-is a respective exchange terminal ET. Suppose the bearer service is STM 64, the link L1 will carry 64 channels so distributed that there are 32 channels in each one of the two opposite directions. Accordingly link L1 carries 32 channel pairs. In the same manner link L2 carries 32 channel pairs. All 32 channel pairs of link L1 but only 16 channel pairs of link L2 are grouped into route R1 which accordingly will hold 48 channel pairs. In the physical transmission system shown in FIG. 2 the remaining 16 link elements of link L2 not used in route R1 may form part of another route, not shown in FIG. 1. In FIG. 2 nodes N1 and N2 correspond to nodes N1 and N2 in FIG. 1.
In FIG. 3 three strata 1, 2, 3 are shown, each such stratum representing a logical view of a non shown physical transport network. Stratum 1 comprises three nodes 10-12, stratum 2 three nodes 20-22, and stratum 3 four nodes 30-33. Stratum 1 comprises three routes 13-15, stratum 2 three routes 23-25 and stratum 3 three routes 34-36. As an example the bearer service at stratum 1 is 64 kbps STM (synchronous transmission mode). As an example the bearer service at stratum 2 is 2 Mbps STM (in the U.S.A. 1.5 Mbps STM). As an example the bearer service at stratum 3 is 155 Mbps STM. As an example routes 13, 14, 15, 25 and 34 are shown to comprise the channel pairs of two links, while routes 23, 24, 35 and 36 are shown to comprise the channel pairs of just one link. A link is indicated by a solid line. The links of route 13 are denoted 40 and 41. At each stratum there are access points to the different networks. These access points are shown schematically by filled points at each stratum. Each access point has a connection to a node in a respective stratum. In stratum 1 the connections from the access points to node 10 are collectively shown at 16, the connections from the access points to node 11 are collectively shown at 17 and those to node 12 are shown at 18. Similar connections 26 and 27 exist at stratum 2. Similar connections 37, 38 at stratum 3 do also exist. Access units are connected to access points. The access units are used for communication. As an example of access units two telephone sets A and B are shown at stratum 1. Access unit are also present at stratum 2 and are symbolically shown at C and D respectively. Examples of access units at stratum 2 are main frame computers. At stratum 3 access units are shown symbolically at E and F respectively. In the non shown physical transport network each one of the connection 16, 17, 18, 26, 27, 28,37, 38, is at its respective node side connected to its respective node by way of an exchange terminal ET. Still speaking in terms of the physical transport network such exchange terminals could be ordinary line interface circuits; LIC:s, in case the bearer service is STM 64 Mbps.
An exchange terminal ET in a stratum is shown as a small unfilled rectangle in the accompanying drawings.
The nodes 10-12 at stratum 1 generally comprise switch fabrics. An exchange in the physical transport network would correspond to one or more switch fabrics in different strata. Cross connectors in the physical transport network would correspond to the nodes 20-22 in stratum 2. Wire connections in the physical transport network would correspond to the nodes 30-33 in stratum 3.
Stratum 1 forms a switched network in the sense that it is possible to route a connection from an originating access unit to a terminating access unit by dialling, at the originating access unit, the telephone number to the terminating access unit. Stratum 2 is generally a non-switched network. A connection from C to D is generally a fixed leased connection which is set up, on a long time basis, by a network operator. Stratum 1 is a non-switched network.
At stratum 1 each route 13, 14, 15 represents a number of resources between two nodes, said resources existing in the form of channel pairs.
The nodes 10, 20 and 30 may or may not correspond to each other depending on the structure of the physical transport network. Generally they do not correspond to each other since their physical counterparts in the physical transport network are located at geographically different sites. The nodes 10, 20 and 30 would correspond to each other if the exchange, the cross connector and the wired connection are all located at the same geographical site. The same considerations apply for nodes 11, 21, 31 and for nodes 12, 22, 32.
The items described above together make up a traffic system. The traffic at each stratum varies depending on the time of the day, the day of the week and may also depend on other criterions. As an example a head office of a company that has sales offices in several cities wants the sale offices to report back to the head office all items sold during a day. The corresponding information should be sent to the head office during nighttime. The time it takes to complete such a data transmission may be unacceptably long if transmission takes place using the bearer service at the stratum 1 level. This is so because of the restricted bandwidth offered by the 64 kbps STM network. Instead the company has leased a number of 2 Mbps connections connecting the sales offices with the head office. The 2 Mbps connections are set up in stratum 2 by the network operator of stratum 2. Such set up is done manually by the network operator with the aid of an operating and support system, OSS, 29. The leased 2 Mbps connections at stratum 2 are set up nighttime between for example 8 pm and 5 am. At daytime said leased connections at stratum 2 are used for other traffic. In this manner the network operator reconfigures the resources of stratum 2 at predetermined times in order to make use of his resources as efficiently as possible. The OSS 29 controls and monitors the operation of the nodes and routes at stratum 2. There is also an OSS 39 for controlling and monitoring the corresponding items at stratum 3.
Manual set up of connections at stratum 2 at predetermined times is a rigid method of meeting the traffic demand from users. The users must notify the network operator of their demands and the network operator must set up the connections manually. Should a user need to use a leased connection at other times than agreed upon the network operator must be contacted. The network operator then has to examine the current traffic situation in stratum 2, assign a link to the requesting user and manually set up the connection for a fixed time period. The time delay between custom demand and set up of a demanded connection may take days.
Since the connections at stratum 2 are leased for fixed time periods and since the traffic demand may change during said fixed time periods the network resources of the physical network are not used efficiently.
U.S. Pat. No. 5,058,105, U.S. Pat. No. 5,182,744, U.S. Pat. No. 5,031,211 relate to methods and devices for enhancing the reliability of a communication network so that traffic which is disrupted by, for example, a faulty link, may quickly be restored to service. Various methods are described for determining alternate routes to which the disrupted traffic is transferred.
U.S. Pat. 4,669,113 relates to a nonhierarchial switching system employing an algorithm for developing link sizes for paths that connect switches in the switching system. This is achieved by having each switch in the switching system to send idle trunk information to a central integrated network controller on a periodic, for example 5-second, basis when trunk status changes occur, i.e. idle trunks are created or removed. Based on the received traffic information the integrated network controller determines the required number of trunks for each link using a process that adjusts for the traffic handling capacity between nodes based on the availability of alternate routes.
EP-A2-464 283 relates to allocating a limited common resource, such as trunks for video conferencing, among a plurality of demands for the resource. An allocation methodology is shown which makes it possible to allocate the bandwidth of a communication path in the network among a plurality of customer demands for that bandwidth. Examples of customer demands for a conference are start time, stop time, maximum bandwidth and minimum bandwidth. To each conference reservation there is associated "binding" comprising a four-tuple of the form (X1, X2, X3, X4) where X1 and X2 refer to specific positions within the bandwidth of the communication path and X3 and X4 refer to the start time and stop time respectively of the conference. A customer site represents one or more endpoints. An allocation arrangement receives demands from a customer site for allocating the network for a communication among a plurality of customer sites. The allocation arrangement stratifies the received demands in response to a grouping of endpoints to be conferenced and can then allocate the network resources in response to the stratified demand. Accordingly the allocation process takes place at predetermined points of time in accordance with a customer's demands and is not driven by the current traffic load.
In Ericsson Review, Vol. 67, Nr. 4, Dec. 1990, Stockholm, Walter Widl, "Telekommunikationsnatets arkitektur", p 148-162 there is described how a telecommunication network is given a layered structure in respect to transmission. A number of static connections are shown. In particular there is shown how information, relating to a connection, is flowing in the various layers. The article does not describe how and when the connections are set up.